A Continuous Nonlinear Sliding Mode Control with Fractional Operators for Quadrotor UAV Systems in the Presence of Disturbances

This paper investigates the robust continuous fractional-order nonlinear sliding mode (RCFONSM) control scheme for controlling a disturbed uncertain quadrotor (DUQ). First, the fractional-order nonsingular terminal sliding mode (FONTSM) manifolds are designed for the altitude and attitude, and a finite-time convergence is realized in the sliding mode phases of the DUQ system. Then, based on fast terminal sliding, reaching laws are proposed to enhance the tracking performance against disturbances and ensure finite-time convergence in the reaching phases of the DUQ system. The proposed robust continuous fractional-order nonsingular terminal sliding mode (RCFONTSM) switch element may effectively improve the dynamical performance of the fractional-order nonlinear sliding mode (FONSM) surface by substituting the integral and derivative operators with fractional-order operators for the error dynamics. The Lyapunov theory is used to prove the stability of the tracking errors and the stabilization of the DUQ simultaneously. The proposed sliding manifolds and fast reaching laws ensured good robustness against disturbances/uncertainties, fast convergence, and high precision. Numerical simulation of the proposed controller compared with fractional-order (FO) backstepping sliding mode control (SMC) is given to demonstrate the superiority of the RCFONSM.